(710b) Theoretical Simulation and Experimental Results On Multilayer Enhanced Infrared Reflection Absorption Spectroscopy (MEIRAS); a Novel In-Situ Technique to Study CO Adsorption and Oxidation On Thin Film Model Pt Catalysts

Deshlahra, P., University of Notre Dame
Wolf, E. E., University of Notre Dame

Multilayer Pt/SiO2/Au and Pt/TiO2/Au structures have been prepared as model catalysts for CO oxidation studies. These structures consist of ultrathin (around 5 nm) Pt films on SiO2 or TiO2 dielectric with a reflecting Au film underneath. We demonstrate that, by appropriately matching the thickness of the dielectric interlayer with the infrared wavelength of interest, we can create optical interference effects that significantly enhance the sensitivity of IRAS technique [1]. This sensitivity enhancement effect is explained through theoretical simulation of reflection of infrared on such multilayer structures [2] based on the well known Fresnel's reflection coefficients [3]. The sensitivity enhancement through multilayer reflection provides unique opportunities for high pressure FTIR study of adsorption and reactions on model catalysts. Unlike commonly used techniques for these studies (such as PM-IRAS and SFG), this technique does not require additional optical instrumentation apart from a standard FTIR setup. Moreover, it is sensitive to both surface normal and tangential vibrational modes. This is in contrast to IRAS techniques on reflecting metal substrates which only detect normal modes. This technique is used for CO adsorption and oxidation study on Pt thin film under actual reaction conditions [4]. Changes in the CO adsorption spectra were observed with change in the film morphology (observed with SEM) due to different sample pretreatments. Ignition behavior of CO oxidation reaction was studied by temperature programming and O2 concentration programming. A repeatable change in shape of the baseline of the spectra was observed as a rough measure of the change in surface oxygen coverage before and after ignition.

[1] P Deshlahra, B Tiwari, LE Ocola, GH Bernstein and EE Wolf, Surf. Sci., 604 (2010), p79 [2] P Deshlahra and EE Wolf, in preparation [3] OS Heavens, Rep. Prog. Phys., 23 (1960), p1 [4] P Deshlahra, K Pfeifer, GH Bernstein and EE Wolf, Submitted to Appl. Catal. A